Applicants claim priority under 35 U.S.C. xc2xa7119 of GERMAN Application No. 199 22 216.9 filed on May 14, 1999. Applicants also claim priority under 35 U.S.C. xc2xa7120 of PCT/DE00/00258 filed on Jan. 27, 2000. The international application under PCT article 21(2) was not published in English.
The invention relates to a device for controlled transmission of sound from an intake tract of an internal combustion engine to an interior of the vehicle having the features of the definition of the species of the main claim.
German Patent 42 33 252 C1 describes such a sound transmission device where a hollow transmitting body formed by a tube communicates at the input end with the intake tract of the internal combustion engine. At the output end, the sound transmitting body, which is designed as a tube, has a diaphragm which, with the known sound transmission device, makes it possible for the sound transmitting body to radiate sound at the output end to the interior of the vehicle. The sound radiating power that can be achieved with such a sound transmission device is relatively low, so it is necessary for the transmission end of the tub having the diaphragm at the output end to pass through a front transverse wall or end wall or spray wall of the vehicle, separating the interior of the vehicle from an engine space containing the internal combustion engine. The transmission tube can thus radiate sound directly through the diaphragm and into the interior of the vehicle to achieve the desired noise effect in the interior of the vehicle. It is thus relatively complicated to assemble the known sound transmission device in a vehicle.
The present invention is concerned with the problem of providing an embodiment having an improved sound radiating power for a sound transmission device of the type defined in the preamble.
This problem is achieved according to this invention by a sound transmission device having the features of claim 1.
This invention is based on the general idea of designing a resonator which has a resonant effect in a desired frequency or frequency band due to a significant increase in cross section within the path of the sound in the sound transmitting body. Due to this resonance, sound energy from the intake tract can be absorbed within the desired frequency range and sent through the resonator to the interior of the vehicle. The sound radiating power of the sound transmission device is thus improved.
According to a preferred embodiment, a line section of the sound transmitting body is designed as a xcex3/2 resonator, where the output end of this line section is sealed with a diaphragm. Two resonators are connected in series in this way, increasing the acoustic power that can be withdrawn from the intake track and radiated toward the interior of the vehicle. However, a design with such a xcex3/2 resonator is a disadvantage when relatively low frequencies must be radiated especially intensely. In a sporty vehicle, for example, acoustic feedback in the range of approximately 250 Hz is perceived as especially attractive by the driver of the vehicle. The length of the xcex3/2 resonator must then be approximately 1.20 meters at a sound velocity of approximately 300 m/s. Therefore, it is relatively complicated to accommodate a line section designed as a xcex3/2 resonator in the engine compartment, because there is usually very little available space in the engine compartment.
A significant improvement is obtained with an alternative refinement wherein a chamber section of the sound transmitting body has a diaphragm bordering in the chamber section a first chamber communicating with the line section. These features make it possible to design the resonator as a so-called xe2x80x9cHelmholtz resonator.xe2x80x9d With such a Helmholtz resonator, the air volume enclosed in the first chamber functions acoustically as a xe2x80x9cspringxe2x80x9d while the line section functions acoustically as a xe2x80x9cmassxe2x80x9d which couples the first chamber to the sound field of the intake tract. This yields an oscillating spring-mass resonance system which resonates especially strongly with sound excitation in the range of the resonant frequency, thus making it possible to pull an especially high radiant energy from the sound field and radiate it through the resonator and into the interior of the vehicle. An especially advantageous embodiment of this invention is obtained when the line section is relatively short, so that the volume of the line section is much smaller than the volume of the first chamber. The resonant properties of the Helmholtz resonator are improved by this measure.
The embodiment of the resonator designed with an enlarged cross section as a Helmholtz resonator results in such a great increase in power that as a rule, a cutout through the front wall of the vehicle and the assembly costs associated with this are unnecessary.
It is especially advantageous if the diaphragm forms an airtight seal on the output end of the sound transmitting body, so that it is possible to connect the sound transmitting body to the input end of the intake tract on the clean end. The input end of the sound transmitting body and/or the line section is preferably connected to the clean end of an air filter of the intake tract or to an air collector from which intake air is distributed to the individual cylinders of the internal combustion engine, or it is connected to a connecting line which connects the air filter to the air collector.
To improve the sound radiation of a certain frequency or frequency band, the chamber section may have at its output end a tube section having a smaller cross section than the cross section of the chamber, where the diaphragm in the chamber section borders a second chamber communicating with the tube section. The resulting resonance system is influenced by this measure, so higher frequency vibrations can be absorbed. The transmission ratio of the resonance system can be adjusted by a suitable choice of the volume of the first chamber relative to the volume of the second chamber. Measures for damping of the resonance system may consist, for example of providing a baffle having a baffle cross section in the tube section, for example, where the baffle cross section is smaller than the tube cross section. The damping of the resonance system can be influenced through the choice of the baffle cross section. In addition, the tube section may be designed at its outlet as a widening funnel, so that an improvement in the sound radiating power is also achieved here. The transmission properties of the resonance system can also be influenced through a controlled choice of the diaphragm, e.g., with regard to weight, size, shape and/or rigidity.
Other important features and advantages of the sound transmission device according to this invention are derived from the subordinate claims, the drawings and the respective description of figures on the basis of the drawings.
It is self-evident that the features mentioned above and to be explained further below can not only be used in the combination indicated here but also in any other combinations or by themselves without going beyond the scope of the present invention.